Modified triplets with reduced secondary spectrum

ABSTRACT

A printer lens consists of a middle negative biconcave component surrounded by two positive doublets, with the lens parameters being selected to reduce secondary spectrum.

United Stat Melech [54] MODIFIED TRIPLETS WITH REDUCED SECONDARY SPECTRUM [72] Inventor: Charles J. Melech, Rochester, N.Y.

[73] Assignee: Eastman Kodak Company, Rochester.N.Y.

[22] Filed: Oct. 1, 1971 [2i] Appl.No.: 185,630

[52] US. Cl ..350/227 [51] Int. Cl. ..G02b 9/26 [58] Field of Search ..350/226, 227

[56] References Cited UNITED STATES PATENTS 2,279,384 4/1942 Altman .'...Ii 50/227 [151 3,692,386 [451 Sept. 19, 1972 Warrnisham et al ..350/227 Tronnier ..350/226 X Primary Examiner-John K. Corbin Attorney-W. H. J. Kline [571 I ABSTRACT A printer lens consists of a middle negative biconcave component surrounded by two positive doublets, with the lens parameters being selected to reduce secondary spectrum.

3 Claims, 1 Drawing Figure P ATENTED 19 I972 3.692.386

CHARLES J. MELECH INVENTOR.

BY zz' ORNEYS CROSS REFERENCE TO RELATED APPLICATIONS Reference is made to commonly assigned and copending US. patent applications; Ser. No. 185,496, entitled Lens With Reduced Secondary Spectrum, filed Oct. 1, 1971, in the name of W. H. Price; Ser. No.

185,602, entitled Printer Lens, filed Oct. 1, 1971, in the name of W. H. Vangraafeiland.

BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to lenses and in particular to modified triplets with reduced secondary spectrum which may be used in printers.

2. Description of the Prior Art Secondary spectrum is the inability of a lens, even when corrected for longitudinal chromatic aberration, to focus all wavelengths of light at the same point. In a design which improves only the monochromatic aberration corrections of an achromatized lens, secondary spectrum becomes the limiting aberration of the lens. 1n monochromatic prints, secondary spectrum tends to reduce the contrast of the final print, particularly in fine detail areas. In color prints, secondary spectrum is manifested as a spreading of color from dark areas into adjacent light areas, a phenomenon known as color fringing or halo.

1t has been known to use modified triplets of the type having two outer positive components surrounding'a middle negative component for photographic printing lenses. Many such lenses are well corrected for monochromatic and longitudinal chromatic aberration. Secondary spectrum is limited in such triplets by careful selection of the materials used in each element of the triplet. Examples of such materials may be found in U.S. Pat. Nos. 2,645,154 and 2,645,156.

SUMMARY OF THE INVENTION An object of the present invention is to provide a printer lens having substantially improved secondary spectrum correction.

It is another object of the present invention to provide such a printer lens with improved secondary spectrum correction which also is well corrected for other aberrations such as axial or oblique spherical aberration, coma, field curvature or astigmatism.

These and other objects are accomplished according to this invention by lenses constructed according to the parameters to be set forth more fully in the detailed description of the preferred embodiments presented below.

BRIEF DESCRIPTION OF THE DRAWING In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawing which is a diagrammatic axial cross-section of a printer lens according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT For all purposes of describing or claiming of the invention herein, the term lens shall be used to describe the complete lens and not elements or components thereof. The long conjugate side of the lens is considered the front. in all of the following examples, the lens components are numbered from front to rear with Roman numerals; the lens elements are numbered from front to rear with Arabic numerals. The indexes of refraction N for the D line of the spectrum, the Abbe numbers V, the radii of curvature R, the thicknesses T and the separations S are numbered by subscript from front to rear. Radii of curvature having centers of curvatures to the rear of the surface are considered positive; those with centers of curvature to the front of the surface are considered negative. All parameters are based upon a lens focal length of mm.

In all embodiments of the invention, as illustrated in FIG. 1, component I is a positive doublet consisting of a front positive biconvex element 1 and a rear negative biconcave element 2. Component 1] consists of a negative biconcave element 3. Component III is a rear positive biconvex doublet consisting of a front meniscus negative element 4 concave to the rear and a rear positive biconvex element 5.

Printer lenses which are well corrected for secondary spectrum may be made according to this invention by following the specifications in the examples presented below.

EXAMPLE 1 174.5 F=100mm Mag.=l2.000x

Thicknea or Element N, V, Radius Separation mm mm R,= 35.170 1 1.62005 63.5 T.=l3.784

lie-32.836 2 1.51700 64.5 T,= 2.667

S,=2.056 Re -44.142 3 1.65317 39.7 T -2.074

S,= 3.035 R =314.75 4 1.6537 39.7 'l.= 4.840

EXAMPLE 2 177.09 F=100mm Mag.=7.250x Thickness or Element N, V, Radius Separation mm mm lip-36.418 2 1.51700 64.5 T,=4.645

' S,=2.002 R =-42.253 3 1.65317 39.7 'T,=2.976

Examples 1-3 are similar to each other in optical performance and differ only in the selection of design parameters but each is well corrected for secondary spectrum.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be afiected within the spirit and scope of the invention.

lclaim:

1. A printer lens having a middle negative component surrounded by two positive doublets, said lens being constructed according to the following table:

Thickness or Element N, V, Radius Separation mm mm R,=32.836 2 1.51700 64.5 T,= 2.667 R,=220.47

2.056 Ra -44.142 3 1.65317 39.7 T,= 2.074

S,= 3.035 R =314.75 4 1.65317 39.7 T 4.840

wherein, from front to rear, the lens elements are numbered from l-S, the corresponding indexes of refraction and Abbe numbers are for the D line of the spectrum, the radii are numbered from R, to R the thicknessesare numbered from T, to T, and the air spaces are numbered from S, to 8,.

2. A printer lens having a middle negative component surrounded by two positive doublets, said lens being constructed according to the following table:

Thickneuor Element N, V, Radius Separation mm mm R,- 23.861 5 l.74500. 46.4 T,=4.796

lip-42.009

wherein, from front to rear, the lens elements are numbered from l-5, the corresponding indexes of refraction and Abbe numbers are for the D line of the spectrum, the radii are numbered from R, to R the thicknesses are numbered from T, to T, and the air spaces are numbered from S, to S 3. A printer lens having a middle negative component surrounded by two doublets, said lens being constructed according to the following table:

Thickness or Element N, V, Radius Separation mm mm 2.120 Re -42.913 3 1.65317 39.7 T,= 3.144

SF 3.689 R =35l.12 4 1.65317 39.7 2.304

wherein, from front to rear, the lens elements are numbered from l-5, the corresponding indexes of refraction and Abbe numbers are for the D line of the spectrum, the radii are numbered from R, to R the thicknesses are numbered from T, to T and the .air spaces are numbered from S, to 8,.

I! i i i 2 2 3? UNITED STATES PATENT OFFICE CERTIFICATE OF COEEEQHQ N S Patent No. 3 Dated 1972 Inventor-(s) C. J. Melech It is certified that error appears in the above-identified patent and that aaidletters Pat-enters hereby corrected as shown below:

Column 2, Example 1 Please delete "1.6537" and substitute Element 4 therefor "1.65317"- Column 4, line 27 Please delete 8 and substitute therefor "S 1 Column 4, line 41 Please delete "T 3.144" from the "Radius mm" column and insert "'T 3.144" in the Thickness or Separation mm" column Signed and sealed this 17th day of April 1973.

Attest:

EDWARD M.FLET( IHER,JR. ROBERT GOTTSCHALK Attestlng Officer Commissioner of Patents 

1. A printer lens having a middle negative component surRounded by two positive doublets, said lens being constructed according to the following table: Thickness orElement ND VD Radius Separation mm mmR1 35.17011.62005 63.5 T1 13.784R2 -32.83621.5170064.5 T2 2.667R3 220.47 S1 2.056 R4 -44.14231.6531739.7 T3 2.074R5 33.670 S2 3.035R6 314.7541.6531739.7 T4 4.840R7 26.48351.7450046.4 T5 6.870R8 -45.368 wherein, from front to rear, the lens elements are numbered from 1-5, the corresponding indexes of refraction and Abbe numbers are for the D line of the spectrum, the radii are numbered from R1 to R8, the thicknesses are numbered from T1 to T5 and the air spaces are numbered from S1 to S2.
 2. A printer lens having a middle negative component surrounded by two positive doublets, said lens being constructed according to the following table: Thickness orElement ND VD Radius Separation mm mmR1 32.35211.6200563.5 T1 8.104R2 -36.41821.5170064.5 T2 4.645 R3 107.20 S1 2.002R4 -42.253 31.6531739.7 T3 2.976R5 32.096 S2 2.220R6 218.3641.6531739.7 T4 4.795R7 23.86151.7450046.4 T5 4.796R8 -42.009 wherein, from front to rear, the lens elements are numbered from 1-5, the corresponding indexes of refraction and Abbe numbers are for the D line of the spectrum, the radii are numbered from R1 to R8, the thicknesses are numbered from T1 to T5 and the air spaces are numbered from S1 to S3.
 3. A printer lens having a middle negative component surrounded by two doublets, said lens being constructed according to the following table: Thickness orElement ND VD Radius Separation mm mmR1 36.54411.6200563.5 T1 14.461R2 -32.63221.5170064.5 T2 2.699R3 314.64 S1 2.120R4 -42.913 31.6531739.7 T3 3.144R5 34.025 S2 3.689R6 351.1241.6531739.7 T4 2.304R7 24.73251.7450046.4 T5 7.083R8 -44.503 wherein, from front to rear, the lens elements are numbered from 1-5, the corresponding indexes of refraction and Abbe numbers are for the D line of the spectrum, the radii are numbered from R1 to R8, the thicknesses are numbered from T1 to T5 and the air spaces are numbered from S1 to S2. 